1. Field of the Invention
The present invention relates to an antireflection film and an optical member including an antireflection film.
2. Description of the Related Art
In a lens (transparent substrate) formed of a light-transmitting member such as a plastic, an antireflection film is provided on a light incident surface in order to reduce loss of transmitted light caused by surface reflection.
For example, as an antireflection film to visible light or infrared light, for example, a dielectric multi-layer film or a fine unevenness layer having a surface on which a fine unevenness structure having a shorter pitch than a wavelength of target light is provided is known.
An object of JP2014-21146A is to provide an optical film which can be applied to optical members having various surface shapes and has excellent performance such as wavelength range properties and incidence angle properties, and JP2014-21146A discloses an optical film in which a fine unevenness layer as a second layer is formed over a transparent substrate with a thin layer as a first layer interposed therebetween. In the optical film described in JP2014-21146A, the first layer includes a region in which the refractive index changes continuously or stepwise depending on a change in a composition ratio of a refractive index material in a thickness direction, and specific examples thereof include a film which is formed using a two-source deposition method of titania and silica and a film which is formed using a two-source deposition method of zirconia and silica.
As in JP2014-21146A, JP2014-81522A discloses a configuration in which a fine unevenness layer is formed over a transparent substrate with a transparent thin film interposed therebetween, and discloses an antireflection film which can be manufactured with reduced kinds of materials and is configured to improve productivity. In JP2014-81522A, the transparent thin film includes multiple layers including the same kind of nitride layers and/or oxynitride layers, and examples of the nitride layers include SiN, AlN, and SiAlN, and examples of the oxynitride layers include SiON, AlON, and SiAlON.